/*
Copyright Suzhou Tongji Fintech Research Institute 2017 All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package sm2

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/elliptic"
	"crypto/hmac"
	"crypto/md5"
	"crypto/rand"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"crypto/x509/pkix"
	"encoding/asn1"
	"encoding/pem"
	"errors"
	"hash"
	"io/ioutil"
	"math/big"
	"os"
	"reflect"
)

/*
 * reference to RFC5959 and RFC2898
 */

var (
	oidPBES1  = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 5, 3}  // pbeWithMD5AndDES-CBC(PBES1)
	oidPBES2  = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 5, 13} // id-PBES2(PBES2)
	oidPBKDF2 = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 5, 12} // id-PBKDF2

	oidKEYMD5    = asn1.ObjectIdentifier{1, 2, 840, 113549, 2, 5}
	oidKEYSHA1   = asn1.ObjectIdentifier{1, 2, 840, 113549, 2, 7}
	oidKEYSHA256 = asn1.ObjectIdentifier{1, 2, 840, 113549, 2, 9}
	oidKEYSHA512 = asn1.ObjectIdentifier{1, 2, 840, 113549, 2, 11}

	oidAES128CBC = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 1, 2}
	oidAES256CBC = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 1, 42}

	oidSM2 = asn1.ObjectIdentifier{1, 2, 840, 10045, 2, 1}
)

// reference to https://www.rfc-editor.org/rfc/rfc5958.txt
type PrivateKeyInfo struct {
	Version             int // v1 or v2
	PrivateKeyAlgorithm []asn1.ObjectIdentifier
	PrivateKey          []byte
}

// reference to https://www.rfc-editor.org/rfc/rfc5958.txt
type EncryptedPrivateKeyInfo struct {
	EncryptionAlgorithm Pbes2Algorithms
	EncryptedData       []byte
}

// reference to https://www.ietf.org/rfc/rfc2898.txt
type Pbes2Algorithms struct {
	IdPBES2     asn1.ObjectIdentifier
	Pbes2Params Pbes2Params
}

// reference to https://www.ietf.org/rfc/rfc2898.txt
type Pbes2Params struct {
	KeyDerivationFunc Pbes2KDfs // PBES2-KDFs
	EncryptionScheme  Pbes2Encs // PBES2-Encs
}

// reference to https://www.ietf.org/rfc/rfc2898.txt
type Pbes2KDfs struct {
	IdPBKDF2    asn1.ObjectIdentifier
	Pkdf2Params Pkdf2Params
}

type Pbes2Encs struct {
	EncryAlgo asn1.ObjectIdentifier
	IV        []byte
}

// reference to https://www.ietf.org/rfc/rfc2898.txt
type Pkdf2Params struct {
	Salt           []byte
	IterationCount int
	Prf            pkix.AlgorithmIdentifier
}

type sm2PrivateKey struct {
	Version       int
	PrivateKey    []byte
	NamedCurveOID asn1.ObjectIdentifier `asn1:"optional,explicit,tag:0"`
	PublicKey     asn1.BitString        `asn1:"optional,explicit,tag:1"`
}

type pkcs8 struct {
	Version    int
	Algo       pkix.AlgorithmIdentifier
	PrivateKey []byte
}

// copy from crypto/pbkdf2.go
func pbkdf(password, salt []byte, iter, keyLen int, h func() hash.Hash) []byte {
	prf := hmac.New(h, password)
	hashLen := prf.Size()
	numBlocks := (keyLen + hashLen - 1) / hashLen

	var buf [4]byte
	dk := make([]byte, 0, numBlocks*hashLen)
	U := make([]byte, hashLen)
	for block := 1; block <= numBlocks; block++ {
		// N.B.: || means concatenation, ^ means XOR
		// for each block T_i = U_1 ^ U_2 ^ ... ^ U_iter
		// U_1 = PRF(password, salt || uint(i))
		prf.Reset()
		prf.Write(salt)
		buf[0] = byte(block >> 24)
		buf[1] = byte(block >> 16)
		buf[2] = byte(block >> 8)
		buf[3] = byte(block)
		prf.Write(buf[:4])
		dk = prf.Sum(dk)
		T := dk[len(dk)-hashLen:]
		copy(U, T)

		// U_n = PRF(password, U_(n-1))
		for n := 2; n <= iter; n++ {
			prf.Reset()
			prf.Write(U)
			U = U[:0]
			U = prf.Sum(U)
			for x := range U {
				T[x] ^= U[x]
			}
		}
	}
	return dk[:keyLen]
}

func ParseSm2PublicKey(der []byte) (*PublicKey, error) {
	var pubkey pkixPublicKey

	if _, err := asn1.Unmarshal(der, &pubkey); err != nil {
		return nil, err
	}
	if !reflect.DeepEqual(pubkey.Algo.Algorithm, oidSM2) {
		return nil, errors.New("x509: not sm2 elliptic curve")
	}
	curve := P256Sm2()
	x, y := elliptic.Unmarshal(curve, pubkey.BitString.Bytes)
	pub := PublicKey{
		Curve: curve,
		X:     x,
		Y:     y,
	}
	return &pub, nil
}

func MarshalSm2PublicKey(key *PublicKey) ([]byte, error) {
	var r pkixPublicKey
	var algo pkix.AlgorithmIdentifier

	algo.Algorithm = oidSM2
	algo.Parameters.Class = 0
	algo.Parameters.Tag = 6
	algo.Parameters.IsCompound = false
	algo.Parameters.FullBytes = []byte{6, 8, 42, 129, 28, 207, 85, 1, 130, 45} // asn1.Marshal(asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 301})
	r.Algo = algo
	r.BitString = asn1.BitString{Bytes: elliptic.Marshal(key.Curve, key.X, key.Y)}
	return asn1.Marshal(r)
}

func ParseSm2PrivateKey(der []byte) (*PrivateKey, error) {
	var privKey sm2PrivateKey

	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
		return nil, errors.New("x509: failed to parse SM2 private key: " + err.Error())
	}
	curve := P256Sm2()
	k := new(big.Int).SetBytes(privKey.PrivateKey)
	curveOrder := curve.Params().N
	if k.Cmp(curveOrder) >= 0 {
		return nil, errors.New("x509: invalid elliptic curve private key value")
	}
	priv := new(PrivateKey)
	priv.Curve = curve
	priv.D = k
	privateKey := make([]byte, (curveOrder.BitLen()+7)/8)
	for len(privKey.PrivateKey) > len(privateKey) {
		if privKey.PrivateKey[0] != 0 {
			return nil, errors.New("x509: invalid private key length")
		}
		privKey.PrivateKey = privKey.PrivateKey[1:]
	}
	copy(privateKey[len(privateKey)-len(privKey.PrivateKey):], privKey.PrivateKey)
	priv.X, priv.Y = curve.ScalarBaseMult(privateKey)
	return priv, nil
}

func ParsePKCS8UnecryptedPrivateKey(der []byte) (*PrivateKey, error) {
	var privKey pkcs8

	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
		return nil, err
	}
	if !reflect.DeepEqual(privKey.Algo.Algorithm, oidSM2) {
		return nil, errors.New("x509: not sm2 elliptic curve")
	}
	return ParseSm2PrivateKey(privKey.PrivateKey)
}

func ParsePKCS8EcryptedPrivateKey(der, pwd []byte) (*PrivateKey, error) {
	var keyInfo EncryptedPrivateKeyInfo

	_, err := asn1.Unmarshal(der, &keyInfo)
	if err != nil {
		return nil, errors.New("x509: unknown format")
	}
	if !reflect.DeepEqual(keyInfo.EncryptionAlgorithm.IdPBES2, oidPBES2) {
		return nil, errors.New("x509: only support PBES2")
	}
	encryptionScheme := keyInfo.EncryptionAlgorithm.Pbes2Params.EncryptionScheme
	keyDerivationFunc := keyInfo.EncryptionAlgorithm.Pbes2Params.KeyDerivationFunc
	if !reflect.DeepEqual(keyDerivationFunc.IdPBKDF2, oidPBKDF2) {
		return nil, errors.New("x509: only support PBKDF2")
	}
	pkdf2Params := keyDerivationFunc.Pkdf2Params
	if !reflect.DeepEqual(encryptionScheme.EncryAlgo, oidAES128CBC) &&
		!reflect.DeepEqual(encryptionScheme.EncryAlgo, oidAES256CBC) {
		return nil, errors.New("x509: unknow encryption algorithm")
	}
	iv := encryptionScheme.IV
	salt := pkdf2Params.Salt
	iter := pkdf2Params.IterationCount
	encryptedKey := keyInfo.EncryptedData
	var key []byte
	switch {
	case pkdf2Params.Prf.Algorithm.Equal(oidKEYMD5):
		key = pbkdf(pwd, salt, iter, 32, md5.New)
		break
	case pkdf2Params.Prf.Algorithm.Equal(oidKEYSHA1):
		key = pbkdf(pwd, salt, iter, 32, sha1.New)
		break
	case pkdf2Params.Prf.Algorithm.Equal(oidKEYSHA256):
		key = pbkdf(pwd, salt, iter, 32, sha256.New)
		break
	case pkdf2Params.Prf.Algorithm.Equal(oidKEYSHA512):
		key = pbkdf(pwd, salt, iter, 32, sha512.New)
		break
	default:
		return nil, errors.New("x509: unknown hash algorithm")
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(encryptedKey, encryptedKey)
	rKey, err := ParsePKCS8UnecryptedPrivateKey(encryptedKey)
	if err != nil {
		return nil, errors.New("pkcs8: incorrect password")
	}
	return rKey, nil
}

func ParsePKCS8PrivateKey(der, pwd []byte) (*PrivateKey, error) {
	if pwd == nil {
		return ParsePKCS8UnecryptedPrivateKey(der)
	}
	return ParsePKCS8EcryptedPrivateKey(der, pwd)
}

func MarshalSm2UnecryptedPrivateKey(key *PrivateKey) ([]byte, error) {
	var r pkcs8
	var priv sm2PrivateKey
	var algo pkix.AlgorithmIdentifier

	algo.Algorithm = oidSM2
	algo.Parameters.Class = 0
	algo.Parameters.Tag = 6
	algo.Parameters.IsCompound = false
	algo.Parameters.FullBytes = []byte{6, 8, 42, 129, 28, 207, 85, 1, 130, 45} // asn1.Marshal(asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 301})
	priv.Version = 1
	priv.NamedCurveOID = oidNamedCurveP256SM2
	priv.PublicKey = asn1.BitString{Bytes: elliptic.Marshal(key.Curve, key.X, key.Y)}
	priv.PrivateKey = key.D.Bytes()
	r.Version = 0
	r.Algo = algo
	r.PrivateKey, _ = asn1.Marshal(priv)
	return asn1.Marshal(r)
}

func MarshalSm2EcryptedPrivateKey(PrivKey *PrivateKey, pwd []byte) ([]byte, error) {
	der, err := MarshalSm2UnecryptedPrivateKey(PrivKey)
	if err != nil {
		return nil, err
	}
	iter := 2048
	salt := make([]byte, 8)
	iv := make([]byte, 16)
	rand.Reader.Read(salt)
	rand.Reader.Read(iv)
	key := pbkdf(pwd, salt, iter, 32, sha1.New) // 默认是SHA1
	padding := aes.BlockSize - len(der)%aes.BlockSize
	if padding > 0 {
		n := len(der)
		der = append(der, make([]byte, padding)...)
		for i := 0; i < padding; i++ {
			der[n+i] = byte(padding)
		}
	}
	encryptedKey := make([]byte, len(der))
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(encryptedKey, der)
	var algorithmIdentifier pkix.AlgorithmIdentifier
	algorithmIdentifier.Algorithm = oidKEYSHA1
	algorithmIdentifier.Parameters.Tag = 5
	algorithmIdentifier.Parameters.IsCompound = false
	algorithmIdentifier.Parameters.FullBytes = []byte{5, 0}
	keyDerivationFunc := Pbes2KDfs{
		oidPBKDF2,
		Pkdf2Params{
			salt,
			iter,
			algorithmIdentifier,
		},
	}
	encryptionScheme := Pbes2Encs{
		oidAES256CBC,
		iv,
	}
	pbes2Algorithms := Pbes2Algorithms{
		oidPBES2,
		Pbes2Params{
			keyDerivationFunc,
			encryptionScheme,
		},
	}
	encryptedPkey := EncryptedPrivateKeyInfo{
		pbes2Algorithms,
		encryptedKey,
	}
	return asn1.Marshal(encryptedPkey)
}

func MarshalSm2PrivateKey(key *PrivateKey, pwd []byte) ([]byte, error) {
	if pwd == nil {
		return MarshalSm2UnecryptedPrivateKey(key)
	}
	return MarshalSm2EcryptedPrivateKey(key, pwd)
}

func ReadPrivateKeyFromMem(data []byte, pwd []byte) (*PrivateKey, error) {
	var block *pem.Block

	block, _ = pem.Decode(data)
	if block == nil {
		return nil, errors.New("failed to decode private key")
	}
	priv, err := ParsePKCS8PrivateKey(block.Bytes, pwd)
	return priv, err
}

func ReadPrivateKeyFromPem(FileName string, pwd []byte) (*PrivateKey, error) {
	data, err := ioutil.ReadFile(FileName)
	if err != nil {
		return nil, err
	}
	return ReadPrivateKeyFromMem(data, pwd)
}

func WritePrivateKeytoMem(key *PrivateKey, pwd []byte) ([]byte, error) {
	var block *pem.Block

	der, err := MarshalSm2PrivateKey(key, pwd)
	if err != nil {
		return nil, err
	}
	if pwd != nil {
		block = &pem.Block{
			Type:  "ENCRYPTED PRIVATE KEY",
			Bytes: der,
		}
	} else {
		block = &pem.Block{
			Type:  "PRIVATE KEY",
			Bytes: der,
		}
	}
	return pem.EncodeToMemory(block), nil
}

func WritePrivateKeytoPem(FileName string, key *PrivateKey, pwd []byte) (bool, error) {
	var block *pem.Block

	der, err := MarshalSm2PrivateKey(key, pwd)
	if err != nil {
		return false, err
	}
	if pwd != nil {
		block = &pem.Block{
			Type:  "ENCRYPTED PRIVATE KEY",
			Bytes: der,
		}
	} else {
		block = &pem.Block{
			Type:  "PRIVATE KEY",
			Bytes: der,
		}
	}
	file, err := os.Create(FileName)
	if err != nil {
		return false, err
	}
	defer file.Close()
	err = pem.Encode(file, block)
	if err != nil {
		return false, err
	}
	return true, nil
}

func ReadPublicKeyFromMem(data []byte, _ []byte) (*PublicKey, error) {
	block, _ := pem.Decode(data)
	if block == nil || block.Type != "PUBLIC KEY" {
		return nil, errors.New("failed to decode public key")
	}
	pub, err := ParseSm2PublicKey(block.Bytes)
	return pub, err
}

func ReadPublicKeyFromPem(FileName string, pwd []byte) (*PublicKey, error) {
	data, err := ioutil.ReadFile(FileName)
	if err != nil {
		return nil, err
	}
	return ReadPublicKeyFromMem(data, pwd)
}

func WritePublicKeytoMem(key *PublicKey, _ []byte) ([]byte, error) {
	der, err := MarshalSm2PublicKey(key)
	if err != nil {
		return nil, err
	}
	block := &pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: der,
	}
	return pem.EncodeToMemory(block), nil
}

func WritePublicKeytoPem(FileName string, key *PublicKey, _ []byte) (bool, error) {
	der, err := MarshalSm2PublicKey(key)
	if err != nil {
		return false, err
	}
	block := &pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: der,
	}
	file, err := os.Create(FileName)
	defer file.Close()
	if err != nil {
		return false, err
	}
	err = pem.Encode(file, block)
	if err != nil {
		return false, err
	}
	return true, nil
}
